The spore-forming microorganism Bacillus thuringiensis (B.t.) produces the best-known insect toxin. The toxin is a protein, designated as .delta.-endotoxin. It is synthesized by the B.t. sporulating cell. The toxin, upon being ingested in its crystalline form by susceptible insect larvae, is transformed into biologically active moieties by the insect gut juice proteases. The primary target is insect cells of the gut epithelium, which are rapidly destroyed. Experience has shown that the activity of the B.t. toxin is so high that only nanogram amounts are required to kill susceptible insects.
The reported activity spectrum of B.t. covers insect species within the order Lepidoptera, which is a major insect problem in agriculture and forestry. The activity spectrum also includes the insect order Diptera, wherein reside mosquitoes and blackflies. See Couch, T. L., (1980) "Mosquito Pathogenicity of Bacillus thuringiensis var. israelensis," Developments in Industrial Microbiology, 22:61-67; Beegle, C. C., (1978) "Use of Entomogeneous Bacteria in Agroecosystems," Developments in Industrial Microbiology, 20:97-104.
U.S. Pat. No. 4,771,131 discloses a toxin gene isolated from a strain of Bacillus thuringiensis. This gene encodes a toxin which is active against beetles of the order Coleoptera.
There have been published reports concerning the use of Bacillus thuringiensis preparations for the control of mites. These publications are as follow:
Royalty, R. N., Hall, F. R. and Taylor, R. A. J. 1990. Effects of thuringiensin on Tetranychus urticae (Acari: Tetranychidae) mortality, fecundity, and feeding. J. Econ. Entomol. 83:792-798.
Neal, J. W., Lindquist, R. K., Gott, K. M. and Casey, M. L. 1987. Activity of the themostable beta-exotoxin of Bacillus thuringiensis Berliner on Tetranychus urticae and Tetranychus cinnabarinus. J. Agric. Entomol. 4:33-40.
Vlayen, P., Impe, G. and Van Semaille, R. 1978. Effect of a commercial preparation of Bacillus thuringiensis on the spider mite Tetranychus urticae Koch. (Acari: Tetranychidae). Mededelingen 43:471-479.
In the above published studies, the active ingredient in the B.t. preparations was beta-exotoxin (also called thuringiensin).
U.S. Pat. No. 4,695,455 concerns methods and compositions for preparing and using biological pesticides, where the pesticides are encapsulated in non-proliferating cells.
U.S. Pat. No. 4,849,217 concerns B.t. isolates active against the alfalfa weevil.